Censorship plays a very important part in a totalitarian state. The state doesn't want people to think for themselves; it wants to keep them in a state of subjection and do as they're told. To make it easier to control people, the state controls what they read. Anything that smacks of subversion or has the potential to give people ideas about changing the government is deemed unacceptable.
In Brave New World, books and other written materials are subject to rigorous censorship for much the same reason, but with an added twist; it's not just the content of written material that's considered dangerous, but its potential consequences.
It's possible to imagine that, in some totalitarian states, a well-written, well-argued scientific paper would be allowed to be published. But in the World State, the Controller deems such a piece unfit for publication because he doesn't know where its conclusions might lead. Even though he readily concedes that the paper in question is "masterly," he still won't allow it to be published, because it could potentially undermine the stability of society. He doesn't know precisely how, but he's not prepared to take any chances.
Other books, such as the Bible and volumes of poetry, are locked away inside the Controller's safe. These are forbidden books, literature deemed unacceptable by the authorities because they offer people an alternative world to that in which they live, the drug-fueled, hedonistic existence laid out for them by the government.
The reasons behind censorship are much easier to detect here than in the case with scientific papers. However, the overriding purpose of all forms of censorship in the World State is the same: to maintain the overall stability of society.